Semiconductor lasers are attractive for a wide variety of applications including telecommunications, computing systems, optical recording systems and optical interconnection of integrated circuits. Semiconductor lasers provide a compact source of coherent, monochromatic light which can be modulated at high bit rates to transmit large amounts of information.
One difficulty with semiconductor lasers is that their threshold current for lasing I.sub.th and their quantum efficiency is dependent on temperature. As a consequence thermal-electric coolers are typically required. However, for many applications, such as data links and fiber-to-the-home, thermal coolers are unduly expensive, and other means of reducing temperature dependence must be found.
The temperature dependence of threshold current of a semiconductor laser is customarily described by the empirical expression: EQU I.sub.th (T)=.alpha.exp(T/To),
where To is a curve-fitting constant characteristic of the laser material system and the laser design. For 1.3-1.55 micrometer wavelength InGaAsP/InP lasers, To is about 50K for both bulk active double heterostructure lasers and for multiquantum well lasers. While it was hoped that the multiquantum well lasers would exhibit a higher To and hence reduce temperature dependence, no significant increase in To has thus far been observed. Accordingly, there is a need for a semiconductor laser having reduced temperature dependence.